Quasi-cleavage Processes Driven by Dislocation Pileups

The present paper explores quasi-cleavage processes driven by dislocation pileups against a Dislocation Free Zone (DFZ). The nanoscopic growth of the main crack consists of sequences of nanocrack formation in DFZ and its subsequent linkage with the main crack. Under mode I loading, the equilibrium locations of individual dislocations and the equilibrium number of dislocations are determined by a minimum energy requirement. Three possible responses are revealed: cleavage without dislocation emission, cleavage after emitting certain amount of dislocations, and cleavage suppressed by incessant dislocation emissions. Accurate dislocations/FEM calculation indicates the emergence of a tensile stress peak ahead of the crack tip, as the dislocations pile up against the DFZ. The stress peak location and the number of emitted dislocations lead to a Crack Tip Opening Angle (CTOA) which is invariant during crack growth. Fracture resistance curves are obtained for quasi-statically growing cracks under the constant CTOA criterion. Copyright Q 1996 Acta Metallurgica Inc.